Van type vehicles for passengers and for cargo are frequently equipped with sliding side doors. Many vans include a single sliding door on the passenger side of the van. However, the van may be equipped with sliding doors on both sides. Drivers and passengers can open or close sliding doors of this type manually from inside or outside of the vehicle. However, the sliding door is usually heavy and often inconvenient and/or difficult to move manually, particularly from inside the vehicle.
For convenience, power operated sliding door closure systems have been developed to allow drivers and passengers to open and close a sliding door virtually effortlessly. Moreover the sliding door usually can be opened or closed from the driver's seat and/or one or more other locations remote from the sliding door.
One type of power operated sliding door closure system, known as a “closed loop” system, is disclosed in U.S. Pat. No. 6,390,535 which issued May 21, 2002 to David Joseph Chapman. The Chapman '535 patent discloses a power operated sliding door closure system in which a sliding door is mounted on a van by travelers that are slidably supported in upper, center and lower tracks. An opening and closing module is mounted inside the van adjacent the center track. A front cable is attached to one end of a cable drive spool and extends from the spool to the traveler via a fixed idler roll. A rear cable is attached to an opposite end of the cable drive spool and extends from the spool to the traveler via another fixed idler roll. A motor drive unit rotates the cable drive spool in one direction to open the sliding door and in an opposite direction to close the sliding door. The closed loop cable closure system disclosed in the Chapman '535 patent also includes two spring biased rollers that are mounted on the vehicle frame between the cable drive spool and the two idler rolls. The spring biased rollers engage the front and rear cables to provide a generally constant tension in the cables.
While the “closed loop” type of system disclosed in the Chapman '535 patent is satisfactory for its intended purpose, the system requires considerable space for the idler rolls and the spring biased rollers. Moreover, one or more of the spring biased rollers may produce reverse bending in the cable which increases fatigue and reduces durability.
Another type of closed loop system is disclosed in the U.S. Pat. No. 6,464,287 granted to Lloyd Walker Rogers, et al. Oct. 15, 2002. The Rogers '287 system includes a guide pulley at one end of a loop of beaded cable and a drive pulley at the opposite end of the loop that drives the beaded cable. The specification of the Rogers '287 patent states that additional guide pulleys can be used. However, a spring biased guide pulley to take up slack in the beaded cable is not shown or describe specifically.